1. Field of Invention
The present invention relates to a method for producing a fluid treatment device having a honeycomb member in a metallic cylindrical housing, with a shock absorbent member wrapped around the honeycomb member, and more particularly a method of producing a catalytic converter for holding a catalyst substrate with a shock absorbent mat wrapped around it in a cylindrical housing.
2. Description of Related Arts
In recent exhaust parts for use in an automotive vehicle, such as a catalytic converter, a diesel particulate filter (abbreviated as DPF) and the like, it is required to hold a catalyst substrate or filter accommodated in a cylindrical housing, firmly. In order to reduce the diameter of the housing to compress an absorbent member after having inserted the catalyst substrate or filter into the housing, a so-called sizing process is getting popular.
With respect to a spinning apparatus capable of forming a necking portion which is at least one of offset from, oblique to and skewed from a body portion (intermediate portion) of a metallic workpiece including the cylindrical housing, Japanese Patent Laid-open Publication No.2001-25826, which corresponds to the U.S. Pat. No. 6,233,993, proposes a method for forming a changed diameter portion of a workpiece by spinning which comprises supporting the workpiece so that a central axis of the portion to be processed is aligned with one of a plurality of forming target axes, the plurality of forming target axes being provided on the basis of a plurality of target processed portions of the workpiece changed from the unprocessed portion to a final target processed portion of the workpiece with a central axis of the final target processed portion being at least one of offset from, oblique to and skewed from a central axis of the unprocessed portion, and molding the portion to be processed by a spinning process so that the central axis of the portion to be processed is matched to each forming target axis of the plurality of forming target axes, and simultaneously changing the diameter of the portion to be processed, in each forming target axis.
As for another spinning apparatus of a type with a workpiece fixed, it is described in Japanese Patent Laid-open Publication No.2002-18539 that a pipe to be formed is clamped by a clamp mechanism, and a drawing tool is movably supported in a radial direction on a tool table mounted on a rotary shaft. With the drawing tool moved in a radial direction, the drawing work is performed. At the same time, by rotating the tip end of the pipe to be formed at a predetermined angle by rotating means, the drawing tool can be applied to the tip end of the pipe which is oblique by the predetermined angle to the axis of the pipe. Also, it is described that the clamping mechanism for the pipe to be formed is provided with moving means for displacing the center line of the pipe to be formed against the center line of the main shaft, and rotating means for rotating it by a predetermined angle, and described that with each means operated, the tip end of the pipe can be held at a desired angle to a working axis.
Also, it is described in Japanese Patent Laid-open Publication No.2002-178045 that according to the prior methods for producing a catalytic converter, as a press machine and a spinning machine are required, each machine costs much and a certain space for placing each machine is required, and that as a workpiece is required to be installed on and removed from each of the press machine and spinning machine, and further required to be transferred from the press machine to the spinning machine, so that its production efficiency is decreased. In order to solve this problem, it is described that stuffing means for stuffing a catalyst substrate having a holding member mounted around its outer periphery, in its axial direction, into a holding cylinder supported on a main shaft, the axial line of which is arranged to be approximately matched with the axial line of the main shaft, on the machine body of the spinning machine for the catalytic converter. And, it is described that the main shaft 53 with its axial line directed to the other end in the horizontal direction is rotatably mounted on the main axis body 52. The main shaft 53 is arranged to be rotated by a driving source such as a motor (not shown). On the tip end of the main shaft 53, is mounted collet chuck 54 having three or four claws, by which the outer periphery of fitting portion 21 of a holding cylinder 2 (material 2′) is clamped to be fixed.
With respect to workpiece clamp means, it is described in an English abstract of Japanese Patent Laid-open Publication No.11-58109 (supplied from the esp@cenet database) that in a collet chuck for a machine tool, which is able to hold or release a work 1, a main body housing 2 is provided with a work inserting hole 3 penetrating up to both front and rear surfaces of the housing 2. A ring-shaped and slotted fastening metal fitting 4, which is able to hold/grip the outer surface of the work 1 that was inserted into the inside of the hole 3, is arranged within the work inserting hole 3. A sliding tool 5 is provided between the work inserting hole 3 and the fastening metal fitting 4. In this case, the sliding tool 5 can slide within the work inserting hole 3 and in the direction of the axis of the hole 3. Thus, the work 1 can be fastened by the fastening metal fitting 4 since the sliding tool 5 fastens the outer surface of the fastening metal fitting 4 inward when the sliding metal fitting 4 slides in one direction, while the fastening to the fitting 4 can be released when the fitting 4 slides in the other direction.
Also, it is described in an English abstract of Japanese Patent Laid-open Publication No.2002-224923 (supplied from the esp@cenet database) that in the pipe clamp unit which receives, fixes, and holds a pipe 4 in a round hole 10a formed by an upper and a lower frames 1 and 2, a plurality of fluid cylinders 11 whose rods are arranged around the round hole 10a of the upper and lower frames 1 and 2 radially towards the center of the round hole, and moving means 13 which move the cylinders in a radius direction of the round hole are provided. And, it is described in an English abstract of Japanese Patent Laid-open Publication No.60-71560 (supplied from the esp@cenet database) that an automatic centering and center rest for positioning so as to stop the advance of a piston rod 32 of a hydraulic cylinder 31 opening or closing this automatic centering and center rest constituted so as to enable two claws 28, 29 to grasp a work W concentrically by means of contact with a cam by a feed screw 37 to be rotated. And, this publication discloses an automatic centering mechanism having the same structure as the one disclosed in Japanese Patent Publication for Opposition No.47-29836 cited as a prior art.
Furthermore, there is disclosed in Japanese Patent Laid-open Publication No.2001-107725, which corresponds to the U.S. Pat. No. 6,381,843, a method for producing a catalytic converter by reducing a diameter of a cylindrical member, together with a shock absorbent member, to hold therein a substrate catalyst, according to a spinning process using a plurality of spinning rollers revolved about the cylindrical member.
According to the apparatuses as disclosed in the Japanese Publication Nos.2001-25826 and 2002-18539, a workpiece (cylindrical housing) is clamped by a clamp device moving horizontally and rotating about a vertical axis, and the spinning process is performed, with the relative positions between the workpiece and the spinning rollers being adjusted. It is required, therefore, to hold the workpiece surely by the clamp device. Especially, in the case where a necking portion is to be formed by the spinning process, on an end portion of the workpiece with its body portion already formed (reduced in diameter), the clamped state of the workpiece becomes an important issue to be observed.
With respect to the method for sizing the cylindrical housing, it is desirable to provide an amount to be reduced in diameter for producing a most appropriate pressure, in view of material error among the substrate, mat and outer cylinder, and then to reduce a part of the outer cylinder holding therein the substrate by that amount. Therefore, the diameter of the outer cylinder formed by the sizing process includes individual error (difference of a few millimeters for ordinary catalytic converter).
Furthermore, with respect to the exhaust parts as described above, generally, the necking process is applied to at least one end portion of the parts, and the spinning process is appropriate for the necking process. The necking process (to the exhaust parts) is a process for reducing the end portion of the outer cylinder (cylindrical housing) in diameter to form a gradually varied diameter (tapered) portion, and form a small diameter cylindrical portion in a body, to be connected with other parts. In case of the necking process, when the spinning process is applied to the end portion of the workpiece with the sizing process applied thereto, it is required to clamp the sized body portion (intermediate portion) of the workpiece by a clamp device. In this case, the body portion has the aforementioned individual error caused in its outer diameter when the sizing process was applied. In general, the clamp device has split dies divided into upper and lower dies, each having a holding surface of a half cylindrical surface, which is hardly follow up the error of even a few millimeters in diameter. Consequently, a clearance is produced due to the difference in radius of curvature between each die and the body portion of the work piece, whereby the contacting area between them is reduced to result in decrease of the clamping force.
According to the prior co-axial spinning process with the workpiece fixed, it is sufficient to prevent the workpiece from rotating and moving axially. Therefore, the aforementioned clamp device may be capable of clamping the workpiece appropriately during the necking process. In contrast, according to the spinning process for forming the end portion of the workpiece to provide the necking portion which is at least one of offset from, oblique to and skewed from the body portion of the workpiece, relatively large clamping force is required comparing with the co-axial spinning process, because bending force and shearing force are applied to the workpiece during the spinning process as described above.
However, according to the spinning apparatus having the prior clamp devices including those as explained above, it is extremely difficult to form the end portion of the workpiece to provide the necking portion which is at least one of offset from, oblique to and skewed from the body portion of the workpiece, holding firmly the body portion of the workpiece which was already formed by the sizing process. For example, although the clamp device as disclosed in the Japanese Publication No.2002-178045 has the same centering function as that of the clamp device having the upper and lower dies, it can not automatically follow up the differences in diameter of the workpieces. Basically, it is of a type for supporting one end of the workpiece, so that it is impossible to penetrate a collet chuck so as to clamp the body portion of the workpiece. In order to apply the necking process to opposite end portions of the workpiece, therefore, it is required to change the arrangement of the clamp device and the workpiece. Thus, even if the prior clamp devices were employed in the prior spinning process, the aforementioned issue could not be solved. Furthermore, although the automatic centering mechanisms as disclosed in the Japanese Publication Nos.6-71560 and No.47-29836 may be used for different objects to be clamped, it is difficult to ensure a sufficient clamping force for clamping the body portion of the workpiece, in the spinning process for forming the end portion of the workpiece to provide the necking portion which is at least one of offset from, oblique to and skewed from the body portion of the workpiece.